The invention relates to a method of killing mature root crop tops prior to harvesting, and to a method of pruning certain perennial crop plants, with minimum adverse impact on the environment. In the past it has been proposed to kill plants with electricity, as shown in U.S. Pat. Nos. 2,007,383, 2,607,165, 2,632,285, 3,543,488, and 3,559,337. It has not previously been recognized, however, that certain root crops can be contacted with electricity to destroy the above-ground portions thereof while not adversely affecting the tubers -- the crop portion -- thereof. This has been recognized according to the present invention, however, and may be utilized to facilitate the harvesting of potatoes, beets, carrots, onions, and the like. According to the present invention, some time before harvesting, after the crops to be harvested are substantially mature, the above ground growth of the crops is contacted with electricity from a high-voltage source, which causes desiccation thereof; for instance for potatoes, the above ground growth is contacted with electricity from a 20 kv source about 10-20 days prior to harvesting, and by the time for harvesting the skin of the potatoes has become more firm, the potatoes are not subject to disease (i.e. leaf roll), and harvesting thereof with conventional equipment is greatly facilitated.
In the past, it has been known to kill the above-ground growth of some root crops -- i.e. potatoes -- prior to harvesting to facilitate the harvesting and firm the skin thereof, but past methods have had a number of drawbacks. For instance, when conventional chemicals are used to kill the above-ground growth, they can and do leave residues which might migrate to the food portion of the crop, and in any event are retained in the soil to some extent and can be assimilated by the next year's crop; if the chemicals are applied too closely to a time when it rains, they may be washed off before they can be effective for killing the above-ground growth and thus a complete wasteful repeat of the application is necessary; dense foliage is not easily penetrated; also; the chemical treatments are often temperature dependent which means that it is not always possible to apply them at the optimum time, and therefore optimum harvesting conditions may not exist. Roto-beating -- that is, actual physical destruction of the above-ground growth -- also is practiced in addition to or in place of chemical application. While roto-beating avoids some of the problems inherent with chemical treatment, it is fairly energy intensive, and is not as completely successful as is the chemical treatment.
It has also not been previously recognized that certain perennial crops -- such as blueberries -- can be pruned with the application of high-voltage electricity, but not destroyed. Conventional proposals for the application of electricity to plants, such as the patents mentioned above, do not recognize that a crop plant may not be killed but merely the above-ground growth thereof destroyed by the application of electricity. According to the present invention, blueberries and like perennial crops, may be treated by the application of electricity -- from a 20 kv source, for instance -- to the above-ground portions thereof every other year to prune the bushes and thereby encourage future growth. Conventionally, pruning of blueberry bushes on a commercial scale is accomplished by burning off of the plants with oilfired burners. While this effectively prunes the plants without serious damage to the root systems, it also destroys much of the organic material in the soil, and is fairly energy intensive.
Thus according to the present invention, the pruning of perennial crops, such as low-bush blueberries, and the destruction of the above-ground growth of root crops, such as potatoes, carrots, onions, and beets, are greatly facilitated by the application of high-voltage electricity to the above-ground portions of the plants. Apparatus such as shown in our U.S. Pat. No. 3,919,806, the disclosure of which is hereby incorporated by reference herein, may be utilized for practicing the method according to the present invention.
It is the primary object of the present invention to provide improved methods for the pruning of certain perennial crops and for facilitating the harvesting of certain root crops, such methods eliminating many of the drawbacks inherent in prior art methods. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.